Thinking you are a bad person for saying no is a symptom of “the disease to please.”

“Saying yes when you need to say no causes burnout. You do yourself and the person making the request a disservice by saying yes all of the time,” says author Duke Robinson.

Here’s how to do the right thing — for yourself and others — in 10 common scenarios where you know that opting out is your best option. Don’t feel guilty. Just take these tips from experts on etiquette and communication — and a cue from your favorite 2-year-old — and say no.

Saying no for the sake of your wallet

1. Request: A friend in need asks for a Trump-worthy loan.

What you should say: “I wish I could, but as a rule, I don’t lend money to friends.”

Why it works: It’s clear that you are not singling out this person as untrustworthy.

Why you shouldn’t feel guilty: Lending any amount of money can cause problems, says communications trainer Don Gabor. “It can change the nature of your relationship if the person doesn’t pay you back.”

How to avoid the situation in the future: Never lend money to friends and you won’t get a reputation as a walking, breathing ATM.

2. Request: A coworker wants you to chip in $25 for a gift for a colleague you wouldn’t recognize at the watercooler.

What you should say: “Oh, I’ve never really had a conversation with Sam. I think I’ll just wish him a happy birthday in person.”

Why it works: Chances are, the person taking donations has no idea how close you are (or are not) with the intended recipient. By clarifying the nature of your relationship — and emphasizing your intention to get to know the person better — you come across as thoughtful rather than cheap.

How to avoid the situation in the future: If workplace gift giving is getting out of hand, take the lead in restoring sanity by circulating a card before someone can break out the gift-donation plate. Make sure others know you don’t expect anything on your birthday. Real Simple: How to manage your anger

What you should say: “We’ve already had to make so many tough decisions to get the guest list down to size. We really can’t squeeze in/afford another guest. But I would love to have you two over for drinks sometime so I can meet him.”

Why it works: If you illuminate some of your behind-the-scenes planning, your cousin may get a clue about the inappropriateness of the request.

How to avoid the situation in the future: Make a few calls before you put together the guest list to see if there are new additions you should consider as you plan. Real Simple: Wedding problems, solved

4. Request: You are offered a promotion that you don’t want. Even though it means more money, it demands more hours and more of what your boss calls responsibility and you call tedium.

What you should say: “I’m flattered that you want me, but for personal reasons I’m not in a situation where I can take this on. Perhaps in a year from now things will be different. Can we talk again if my circumstances change?”

Why it works: If you’re caught in this enviable dilemma, your boss will understand you have personal priorities that take precedence.

Why you shouldn’t feel guilty: By saying no to more time at the office, you’re saying yes to other things you cherish, be they long walks alone at sunset or evening time with your children.

How to avoid the situation in the future: “If a position opens up at your workplace, you could let it be known that you are not in the running,” Breitman suggests. Being forthright saves your manager the trouble of pursuing a candidate who isn’t interested.

5. Request: You are asked to coordinate the bake sale — again — at your child’s school.

What you should say: “I know I’m going to disappoint you, but I’ve decided not to volunteer this year, because I fear I’ll end up feeling resentful. Is there any way to get some of the other parents to step up?”

Why it works: Often people feel manipulated into doing something (“The ice cream social just won’t happen without your help!”). If you can address the problematic pattern of one person’s doing all the work, you sidestep the manipulation. And if you say no, it might force others (who never get asked) to say yes.

Why you shouldn’t feel guilty: “You’ve done your fair share, and now others can do this job,” says Robinson.

How to avoid the situation in the future: “Encourage school leaders to present the problem to all the parents,” says Robinson. “If people know an important program may fail, they’ll usually remedy the situation.”

6. Request: You’re invited to a distant relative’s annual Lobster Luau — for the 14th year in a row.

What you should say: “I’ve really had fun in the past, but I can’t make it this year. That week is already packed for me.”

Why it works: “You’ve explained it in a way that doesn’t sound like a personal rejection,” says Robinson. “And you’ve asked for understanding, based on your need to take stress out of your schedule. Everyone can identify with that.”

Why you shouldn’t feel guilty: You have only so much free time — and so much tolerance for flying lobster goo. “Don’t RSVP yes, then back out at the last minute or, worse, not show up at all,” say Izzo and Marsh. “That is the least decorous way of handling the invite.”

How to avoid the situation in the future: In a note, thank the relative for thinking of you and explain that because you tend to be busy at this time of year, he should feel free to take you off his invite list. Real Simple: Write the perfect thank you note

7. Request: Your boss asks you to supervise this season’s intern — last seen with her feet up on a desk, iPod on, Gameboy in hand.

What you should say: “Wow, that’s an interesting project. I’m really busy with the ABC assignment right now, so let me know if you want me to re-prioritize.”

Why it works: “Asking your boss to prioritize tasks for you means you don’t have to actually say the no word,” Breitman says. If she tells you to just squeeze the new task in, then do it. But keep a list of all the extra work you’ve done — for your next review.

Why you shouldn’t feel guilty: You really do have enough work to do as it is.

How to avoid the situation in the future: If extra tasks keep getting dumped on your desk, ask your boss for a meeting. Explain that the added assignments are making it hard to do your primary job properly. Ask if she wants to review your job description (and renegotiate your salary while she’s at it).

Saying no for the sake of your sanity

8. Request: A friend asks to borrow your car (because hers is in the shop to repair the dent she got while driving, talking on her cell phone, and unwrapping her kid’s juice-box straw).

What you should say: “I don’t lend anything worth more than $1,000.” Try to avoid the old “I don’t have insurance for a non–family member” excuse — most insurance policies cover the car, not specific drivers. (If your friend got into an accident, it could make your premium go up, though.) If you have time, offer her a ride instead.

Why you shouldn’t feel guilty: “Your car is probably the first or second most valuable thing you own,” says Breitman. “You’re protecting a big financial asset.” Plus, if your friend were to get into an accident, your relationship might be totaled, too.

How to avoid the situation in the future: Let your friends know that while you’re typically a generous lender (“Of course you can borrow my snorkeling gear!”), your car is off-limits.

9. Request: A guest offers to bring her seven-layer dip to your party. It doesn’t really go with the Greek theme you have planned. Real Simple: Party planning basics

What you should say: “What a kind offer — thank you. I have already planned the menu, but do you have any dietary restrictions I should know about?” If she’s just asking to be nice and insists on bringing something, suggest a bottle of wine or a loaf of bread.

Why it works: By acknowledging the generosity of the offer, you let that person know she did all she could. Of course, if the person has dietary restrictions that make cooking difficult for you, relent and let her bring a dish she can eat.

Why you shouldn’t feel guilty: The person is most likely offering just to be courteous. By saying no, you give her license to relax and enjoy your hospitality. How to avoid the situation in the future: When you invite people, ask if there is anything they don’t eat, because you want to make sure your menu works for everyone. Emphasize the word menu, so people know that you have a plan or a theme for the meal (and so they won’t try to upset it).

10. Request: Your future sister-in-law wants to throw you a shower, but you don’t want the fuss.

What you should say: “I really don’t want a party, but thank you so much for offering. Why don’t we splurge on a visit to a day spa instead?”

Why it works: “Not everyone likes a party in her honor or wants to be the center of attention with a paper plate of bows on her head,” say etiquette writers Kim Izzo and Ceri Marsh. Unless she has her own agenda, she should understand.

Why you shouldn’t feel guilty: “If you decline, you are taking away some pleasure from the people who care about you, but it is your occasion to shout about or be quiet about,” say Izzo and Marsh.

How to avoid the situation in the future: Announce what you would prefer to do instead of a shower before anyone offers to throw one.